How do I test my home for radon?

Stasis Home Research Every claim on this page is graded against peer-reviewed health research and linked to its primary source.Updated August 2026

Get a short-term test kit, put it on the lowest level you live on, and keep the house closed while it runs. EPA says many kits sell for under $25. There are no signs of radon to notice, so a measurement is the only way to know. If the first result reads 4 pCi/L or higher, test again before you spend anything.

There are no signs. That is the whole reason to test.

One of the most common questions about radon is what the signs are that a house has it. There are none. EPA states it plainly: there are no immediate symptoms from exposures to radon. The gas has no color, no smell, and no taste, and WHO makes the same point from the other direction, that people can unknowingly be living or working in very high levels.

Lung cancer is the only health effect definitively linked to radon exposure, and it would usually appear 5 to 25 years after the exposure that caused it. EPA also states there is no evidence that other respiratory diseases such as asthma are caused by radon. On children, EPA says there is no evidence they face greater risk of radon-induced lung cancer than adults, and its Citizen's Guide adds that there are currently no conclusive data either way. A symptom check on your household tells you nothing about your radon level, in either direction.

You cannot read it off the house either. Radon levels vary greatly from home to home, and levels next door can be very different from yours. Elevated levels have been found in homes in every state. Even EPA's own Map of Radon Zones carries the caveat in writing: it should not be used to determine whether an individual home needs to be tested.

That is a property of the gas, and it is the reason a measurement is the only method that works here.

When to test, and when to test again

Radon peaks in winter is a widely held belief with a real mechanism behind it, but there is no peak month. EPA says indoor radon levels tend to vary from day to day and season to season, and names no month. Neither will we, because no government source publishes one.

Here is the mechanism. Warm air inside a house rises and leaks out high in the building, which leaves the lowest level at slightly lower pressure than the soil beneath it. Soil gas flows up through slab cracks, plumbing penetrations, sump pits, and the joint where the slab meets the wall to fill that vacuum. Heating season makes the pressure difference larger, and a closed-up house cuts the ventilation that would otherwise dilute what comes in. In cold-winter climates, winter readings do tend to run above summer readings. Where winters are mild, that effect is muted and the within-day and barometric swings still apply.

Then there is the counterweight. A 2023 study of 66 homes in four rural Kentucky counties set out to predict indoor radon from geology, season, atmospheric conditions, and topography. It found that seasonality was not associated with indoor radon in that sample, and its authors note that the research on this is mixed. They offer two possible reasons for that null result, and neither is a verdict on the calendar. Participants kept the house closed during both test windows, which is what EPA tells everyone to do anyway. A pandemic delay also pushed the winter window into late spring, so the two seasons were less different than intended.

January is worth naming for a different reason. It is National Radon Action Month, an EPA public-awareness campaign, which is why radon gets its yearly burst of public attention then. Winter is a reasonable time to test because a closed house happens naturally, but the month matters far less than whether you kept the house closed and ran the test long enough.

The triggers that actually call for a test are specific. Test every home before you move in, or soon after, including a home built with radon-resistant features. Test before a major structural renovation such as turning an unfinished basement into living space, and test again once the work is done, because renovations change the level. Retest if your living patterns change and you start occupying a lower level of the house.

A recent build date is not a pass. A tighter, more energy-efficient envelope holds in whatever the soil emits, so newer construction is not automatically lower. EPA is blunt about it: radon turns up in old homes, new homes, drafty homes, insulated homes, homes with basements and homes without them.

The four ways to measure, and the different question each one answers

Three devices and one service, and they answer different questions, which is the part a retail listing cannot tell you. A short-term radon test kit sits in the house between two and 90 days depending on the device.

Most kits run two to seven days. The common device families are charcoal canisters, alpha track detectors, electret ion chambers, charcoal liquid scintillation, and continuous monitors. Because radon levels move day to day and season to season, a short-term test is less likely than a long-term one to tell you your year-round average. It is a screening tool, and the right first move.

A long-term test stays in place more than 90 days, usually an alpha track or electret detector. It is the closest thing to a reading of what you actually breathe across a year. WHO goes further: because concentrations swing from day to day and hour to hour, it prefers at least three months of measurement to estimate an annual mean.

A continuous monitor, sometimes sold as a radon detector, gives you an hourly trace instead of one number at the end. That matters because a single moment's reading is not interpretable on its own. Indoor radon rises overnight and typically peaks in the early morning hours, when ventilation is at its lowest. Readings also run lower when barometric pressure is higher during the test window. The 2023 Kentucky study measured that directly: the odds of a result at or above 4 pCi/L dropped sharply as pressure rose.

Sensing technology matters inside this category. In third-party testing against reference instruments, pulsed ion chambers caught up to a change in radon within one to two hours. Some diffusion-chamber detectors took 8 to 16 hours. On a short deployment we would not lean on the first day of data from the slower type.

A professional test buys you something a kit cannot: a result from somebody with no stake in the sale, which is what the other side usually asks for. A DIY radon test kit bought by mail or at a hardware store is the right tool for finding out where you stand. It stops being the right tool the moment money changes hands. EPA's guide puts it as a choice: if you prefer, or if you are buying or selling a home, you can hire a qualified tester instead.

The credential to ask for is a state license, or a listing with one of the two nationally recognized proficiency programs, the National Radon Proficiency Program (NRPP) or the National Radon Safety Board (NRSB). EPA requires states receiving indoor radon grants to publish lists of credentialed providers only, so a state radon program is a better starting point than a search engine.

Cost is rarely the obstacle. Free kits are sometimes available from local or county health departments and from state radon programs, and some states offer free or discounted kits to the public. Kits are also available from some hardware stores, some American Lung Association chapters, and the National Radon Program Services at Kansas State University, which runs under a cooperative agreement with EPA. No source we could verify publishes a national price for a professional measurement.

Accuracy here is a procedure problem, not a hardware problem. EPA's position is that it expects radon test devices used properly to give accurate and reliable results. What EPA's own instructions guard against is placement, an open window, and a run that was too short, not a defective kit.

How to run the test so the number means something

Placement first, because it is the part of the procedure EPA writes out in the most detail. Put the kit on the lowest lived-in level of the house: the basement if you use it regularly, otherwise the first floor. Put it in a room you actually use, like a living room, playroom, den, or bedroom. Not the kitchen and not the bathroom. Set it at least 20 inches above the floor, somewhere it will not get knocked around, and away from drafts, high heat, high humidity, and exterior walls.

Closed-house conditions are the other half. Close the windows and outside doors and keep them closed as much as you can while the test runs. Normal coming and going is fine. Heating and air conditioning fans that recirculate indoor air can run. What cannot run is a fan or a machine that brings in air from outside. A fan that is part of a radon-reduction system is fine, and so is a small exhaust fan used briefly. If the test only runs two or three days, close the house at least 12 hours before you start it, not at the moment you open the package.

Do not start a two or three day test into a severe storm or an unusually windy stretch. Falling barometric pressure and wind loading both change how hard the house pulls on the soil beneath it, which is what you are trying to measure in its normal state. Wait for the weather to settle.

A qualified measurement professional adds things a mail-in kit does not. They work to the national measurement standard. It sets a minimum run of valid data, and closed-house conditions before and throughout the test. It also fixes where the device goes: the lowest occupied living level, with set clearances from doors, windows, exterior walls, HVAC vents and direct sun. That precision is a large part of why a buyer's side asks for a professional result rather than the seller's mail-in kit.

When the test ends, reseal the package and mail it to the lab printed on it right away, which is EPA's own instruction. Results usually come back in about two weeks.

Two things get tested instead of the air, and should not. The first is water. Soil is usually a much larger radon risk than water, so the air test comes first. A radon-in-water problem is more likely when the source is ground water. That means a private well, or a public system that draws on ground water. It is not usually a problem when the supply is surface water.

The second is a granite countertop or another building material. EPA's position is that building materials rarely cause radon problems by themselves, and the soil under the house is the main source. Either way the test is identical, so measure the room you live in and let the number decide.

Reading the number you get back

EPA publishes a three-step protocol for this and it is worth following exactly, because it is built around the fact that one short test is a screen and not a verdict.

Step one is the short-term test. If it comes back at 4 pCi/L or higher, do not act on it yet. If it comes back below 4 pCi/L, EPA does not call for a follow-up test. That is not the same as a clean bill. EPA's own guide says levels below 4 pCi/L still pose some risk.

Step two is the follow-up. For a better understanding of your year-round average, run a long-term test. If you need an answer quickly, run a second short-term test instead. The higher the first result, the stronger the case for a second short-term test rather than a long one. If the first result is more than twice the 4 pCi/L action level, EPA says to run that second short-term test immediately.

Step three is the decision. Fix the home if a long-term follow-up reads 4 pCi/L or more. If you ran a second short-term test instead, consider fixing if the average of the two is 4 pCi/L or higher.

The reason for the retest is measurement noise, and EPA's own illustration of it is the clearest one to work from. If the average of your two short-term results is 4.1 pCi/L, there is about a 50 percent chance your year-round average is somewhat below 4. A borderline result is a reason to measure again before you spend anything.

Four is EPA's action level. EPA also tells Americans to consider fixing between 2 and 4 pCi/L, and gives one reason for it: there is no known safe level of exposure to radon. The 4 pCi/L line dates to 1986. It was set as a feasibility compromise: the level at which fixing a home is almost always worth what it costs, not the level at which exposure becomes harmless. WHO sets its own reference level lower, at 100 Bq/m3, about 2.7 pCi/L. Risk from radon is continuous. It does not switch on at 4.

The average indoor level in US homes is estimated at about 1.3 pCi/L, and outdoor air normally runs about 0.4 pCi/L. About one home in every 15 in the US is estimated to have an elevated level. Congress set a long-term goal of indoor radon no higher than outdoor air, which is not yet achievable in every case, but most homes today can be brought to 2 pCi/L or below.

Here is what the levels mean for risk, in EPA's own words. Take 1,000 people who never smoked, exposed over a lifetime. EPA's table says about 2 of them could get lung cancer at 1.3 pCi/L, about 7 at 4 pCi/L, about 18 at 10, and about 36 at 20. For people who smoke, the same rows read about 20, about 62, about 150, and about 260 per 1,000.

EPA states that radon and smoking act synergistically. A smoker with a radon problem carries more risk than adding the two together would suggest. EPA's advice to that reader is to do both things, stop smoking and lower the level.

If a confirmed result comes back at 4 pCi/L or higher, there is a settled engineered fix for it. It is a contractor job with its own set of decisions, and it is covered separately. The testing job is finished once you have a number you can trust.

Do I need a radon test for a home inspection?

Rarely by law, usually in practice. There is no federal requirement to test at sale and no federal radon disclosure law like the lead-paint rule, so disclosure is set state by state. Buyers ask anyway, and EPA notes they frequently want the test made by someone not involved in the sale. A buyer may want a fresh one if the last test is older than about two years, if the home has been renovated since, or if they plan to occupy a lower level than the one tested. If you are selling, EPA's advice is to test now, not under a closing deadline.

Can I test for radon in my home myself?

Yes. EPA points people to low-cost do-it-yourself radon test kits sold by mail and in some hardware stores, and says it expects test devices used properly to give accurate and reliable results. Accuracy depends on following the rules: the lowest lived-in level, a room you actually use, not the kitchen or bathroom, at least 20 inches off the floor, and the house kept closed while the test runs. EPA adds that if you prefer, or if you are buying or selling a home, you can hire a qualified tester instead.

How much does a radon test cost?

EPA's factsheet says many test kits are priced under $25. Free kits are sometimes available from state radon programs and local or county health departments, so check there before buying one. A professional measurement costs more than a mail-in kit, and it is what buyers commonly ask for in a sale. No national price is published for a professional test, so treat any figure you are quoted as a local price.

Where do I start?

Check whether your state radon program or county health department offers a free or discounted kit before you buy one.
Put the test on the lowest level you actually live on, in a room you use, not the kitchen and not the bathroom, at least 20 inches above the floor.
Keep it away from drafts, high heat, high humidity, exterior walls, and anywhere it might get knocked around.
Close the windows and exterior doors and keep them closed. For a two or three day test, close the house 12 hours before you start it.
Let recirculating heating and cooling run, and shut off anything that pulls air in from outside for the length of the test.
Skip a short test during a severe storm or unusually high winds, and start it again once the weather settles.
Reseal the kit and mail it to the lab the day the test ends. Results usually come back in about two weeks.
If the result reads 4 pCi/L or higher, test a second time before you spend anything. If it reads more than double that, run the second test right away rather than waiting on a long-term one.

What does the science say?

AIRRadon The substance itself: how it gets in, why the damage lands in the lung, and what the thresholds are graded against.AIRCarbon dioxide (CO2) The other thing a tight, closed-up house accumulates, and the cheapest signal that a home is under-ventilated.WTRRadionuclides (uranium, radium) If you are on a private well, the other things local geology puts into water that a radon air test will not see.

What actually works?

Method

Radon mitigation (sub-slab depressurization)

Common questions

What are the signs your house has radon?

There are none. Radon has no color, no smell, and no taste, and EPA states directly that there are no immediate symptoms from exposures to radon. Lung cancer is the only health effect definitively linked to it, and it would usually appear 5 to 25 years after the exposure. You cannot infer it from the house or the neighborhood either, because levels vary greatly between homes and even between houses next door. Testing is the only way to know.

What month is radon the highest?

No government source names a peak month. EPA says levels vary from day to day and season to season without naming one. The winter mechanism is real: heating season increases the pressure difference that draws soil gas into a house, and a closed-up house dilutes less of it. But a 2023 study of 66 homes in rural Kentucky found no association between season and indoor radon in that sample. January draws attention because it is National Radon Action Month, an EPA awareness campaign, not because it is a measured peak.

Are free radon test kits real?

Yes, sometimes. EPA states that free test kits are sometimes available from local or county health departments or from state radon programs, and that some states offer free or discounted kits to the public. Availability changes and varies by state, so the place to check is your own state radon program, whose contact information EPA publishes. Kits are also available from some hardware stores, some American Lung Association chapters, and the National Radon Program Services at Kansas State University, which operates under a cooperative agreement with EPA.

What is the difference between a short-term and a long-term radon test?

Duration, and what the result actually means. A short-term test stays in the home between two and 90 days, most commonly two to seven, and gives you a screening number. A long-term test stays more than 90 days and is far more likely to reflect your true year-round average, which is what your exposure depends on. WHO prefers at least three months of measurement to estimate an annual mean. Short-term testing is the right tool when a decision is on a clock, such as a home sale or checking whether a mitigation system works.